Bug 382369. Distinguish click from click-drag on a <label> so text selection works. r+sr=roc, help from Zack Weinberg

content/base/src/nsGkAtomList.h

@@ -1663,6 +1663,7 @@ GK_ATOM(viewProperty, "ViewProperty")
 
 // Content property names
 GK_ATOM(genConInitializerProperty, "QuoteNodeProperty")
+GK_ATOM(labelMouseDownPtProperty, "LabelMouseDownPtProperty")
 
 // Languages for lang-specific transforms
 GK_ATOM(Japanese, "ja")

content/html/content/src/nsHTMLLabelElement.cpp

@@ -44,10 +44,8 @@
 #include "nsPresContext.h"
 #include "nsIFormControl.h"
 #include "nsIForm.h"
-#include "nsIDOMHTMLDocument.h"
-#include "nsIDOMXULDocument.h"
+#include "nsIDOMDocument.h"
 #include "nsIDocument.h"
-#include "nsIFormControlFrame.h"
 #include "nsIPresShell.h"
 #include "nsGUIEvent.h"
 #include "nsIEventStateManager.h"
@@ -209,12 +207,23 @@ EventTargetIn(nsEvent *aEvent, nsIContent *aChild, nsIContent *aStop)
   return PR_FALSE;
 }
 
+static void
+DestroyMouseDownPoint(void *    /*aObject*/,
+                      nsIAtom * /*aPropertyName*/,
+                      void *    aPropertyValue,
+                      void *    /*aData*/)
+{
+  nsIntPoint *pt = (nsIntPoint *)aPropertyValue;
+  delete pt;
+}
+
 nsresult
 nsHTMLLabelElement::PostHandleEvent(nsEventChainPostVisitor& aVisitor)
 {
   if (mHandlingEvent ||
       (!NS_IS_MOUSE_LEFT_CLICK(aVisitor.mEvent) &&
-       aVisitor.mEvent->message != NS_FOCUS_CONTENT) ||
+       aVisitor.mEvent->message != NS_FOCUS_CONTENT &&
+       aVisitor.mEvent->message != NS_MOUSE_BUTTON_DOWN) ||
       aVisitor.mEventStatus == nsEventStatus_eConsumeNoDefault ||
       !aVisitor.mPresContext) {
     return NS_OK;
@@ -224,8 +233,49 @@ nsHTMLLabelElement::PostHandleEvent(nsEventChainPostVisitor& aVisitor)
   if (content && !EventTargetIn(aVisitor.mEvent, content, this)) {
     mHandlingEvent = PR_TRUE;
     switch (aVisitor.mEvent->message) {
+      case NS_MOUSE_BUTTON_DOWN:
+        NS_ASSERTION(aVisitor.mEvent->eventStructType == NS_MOUSE_EVENT,
+                     "wrong event struct for event");
+        if (static_cast<nsMouseEvent*>(aVisitor.mEvent)->button ==
+            nsMouseEvent::eLeftButton) {
+          // We reset the mouse-down point on every event because there is
+          // no guarantee we will reach the NS_MOUSE_CLICK code below.
+          nsIntPoint *curPoint = new nsIntPoint(aVisitor.mEvent->refPoint);
+          SetProperty(nsGkAtoms::labelMouseDownPtProperty,
+                      static_cast<void *>(curPoint),
+                      DestroyMouseDownPoint);
+        }
+        break;
+
       case NS_MOUSE_CLICK:
         if (NS_IS_MOUSE_LEFT_CLICK(aVisitor.mEvent)) {
+          const nsMouseEvent* event =
+            static_cast<const nsMouseEvent*>(aVisitor.mEvent);
+          nsIntPoint *mouseDownPoint = static_cast<nsIntPoint *>
+            (GetProperty(nsGkAtoms::labelMouseDownPtProperty));
+
+          PRBool dragSelect = PR_FALSE;
+          if (mouseDownPoint) {
+            nsIntPoint dragDistance = *mouseDownPoint;
+            DeleteProperty(nsGkAtoms::labelMouseDownPtProperty);
+
+            dragDistance -= aVisitor.mEvent->refPoint;
+            const int CLICK_DISTANCE = 2;
+            dragSelect = dragDistance.x > CLICK_DISTANCE ||
+                         dragDistance.x < -CLICK_DISTANCE ||
+                         dragDistance.y > CLICK_DISTANCE ||
+                         dragDistance.y < -CLICK_DISTANCE;
+          }
+
+          // Don't click the for-content if we did drag-select text or if we
+          // have a kbd modifier (which adjusts a selection), or if it's a
+          // double click (we already forwarded the first click event).
+          if (dragSelect || event->clickCount > 1 ||
+              event->isShift || event->isControl || event->isAlt ||
+              event->isMeta) {
+            break;
+          }
+
           if (ShouldFocus(this)) {
             // Focus the for content.
             aVisitor.mPresContext->EventStateManager()->